1. Field of the Invention
The present invention relates to a control system for an automatic transmission for a vehicle, wherein a manual shifting can be carried out in addition to an automatic shifting based on a usual shifting map.
2. Description of the Related Art
There is a conventionally known automatic transmission designed so that an optimal gear shift stage is selected by searching a shifting map using, as parameters, detection values such as vehicle speed, engine load and the like, and an automatic shifting is conducted to establish such optimal gear shift stage. In such an automatic transmission, shifting characteristics are established on the basis of the general travel state of the vehicle. For this reason, the following problem is encountered: it is difficult to select the optimal gear shift stage in all travel states, and a throttle opening degree and an amount of accelerator pedal depression are detected, but eventually, the gear shift stage is uniformly selected. There are also conventionally known automatic transmissions in which a shifting characteristic emphasizing a power performance and a shifting characteristic emphasizing a specific fuel consumption can be selected. In any of these automatic transmissions, however, a shifting characteristic suitable for the driver's preference is rarely completely realized.
Therefore, automatic transmissions have been proposed which are designed so that any gear shift stage can be selected by operating a switch or a lever by a driver (see Japanese Patent Application Laid-open No. 37359/84, 8545/90 and 125174/90).
There are also conventionally known automatic transmissions designed so that the operating hydraulic pressure for the hydraulic engage elements in a transition period of shifting is controlled by a solenoid valve such as a linear solenoid and a duty solenoid, based on a previously established shifting characteristic and travel conditions such as a throttle opening degree and a vehicle speed (see Japanese Patent Application Laid-open No. 224553/89 and 215157/87).
The control Of the hydraulic pressure in the known technique is extremely effective, when the shifting is conducted based on the previously established shifting characteristics in the automatic shifting mode. However, when the manual shifting mode, in which the driver operates the switch or the lever to conduct the shifting as desired, has been established, the amount of data accommodating all shifting points is very large and hence, it is difficult to realize the control of the hydraulic pressure.